The field of art to which this invention pertains is desulfurization of hydrocarbon feedstocks to low levels of sulfur. Hydrodesulfurization processes have been used by petroleum refiners to produce more valuable hydrocarbonaceous streams such as naphtha, gasoline, kerosene and diesel, for example, having lower concentrations of sulfur and nitrogen. Feedstocks most often subjected to hydrotreating or desulfurization are normally liquid hydrocarbonaceous streams such as naphtha, kerosene, diesel, gas oil, vacuum gas oil (VGO) and reduced crude, for example. Traditionally, hydrodesulfurization severity is selected to produce an improvement sufficient to produce a marketable product or a suitable feedstock for downstream processing. Over the years, it has been recognized that due to environmental concerns and newly enacted rules and regulations, saleable products must meet lower and lower limits on contaminants such as sulfur and nitrogen. Recently new regulations were proposed in the United States and Europe which basically require the complete removal of sulfur from liquid hydrocarbons which are used as transportation fuels such as gasoline and diesel.
Desulfurization is generally accomplished by contacting the hydrocarbonaceous feedstock in a desulfurization reaction vessel or zone with a suitable desulfurization catalyst under conditions of elevated temperature and pressure in the presence of hydrogen to yield a product containing the desired maximum limits of sulfur. The operating conditions and the desulfurization catalysts within the desulfurization reactor influence the quality of the desulfurized products.
Although a wide variety of process flow schemes, operating conditions and catalysts have been used in commercial desulfurization activities, there is always a demand for new desulfurization methods which provide lower costs and the required product quality. With the mandated low sulfur transportation fuels, the process of the present invention greatly improves the economic benefits of producing low sulfur fuels.